The present invention relates to devices for the distribution of electric power and more particular to electrically connecting a wire or conductor to a terminal using a clamping screw.
Bus bars and neutral terminal bars of panel boards and similar electrical apparatus are often connected to the power supply wires or conductors by lugs and screws. When the panel board has a great number of circuits, a large number of lugs and screws are required. For example, a forty circuit panel board may require one-hundred and fifty or so screws. Conventionally, the electrical connection for securing a conductor to a neutral terminal bar is accomplished by providing a plurality of threaded apertures in the terminal bar. A bore is disposed transversely with respect to each threaded aperture. When making the electrical connections, the conductor is inserted into each bore and a clamping screw is inserted into the associated threaded aperture. The screw is then tightened to secure the conductor in the bore, making the electrical connection.
After the manufacture of an electrical device which includes a plurality of clamping screws which are intended to enable the future connection of the electrical conductors to the device by the end user, the screws are typically screwed all the way down into in their respective threaded apertures. Conventionally, the screws are factory torqued to generally 20 inch-pound which precludes subsequent loosening thereof by vibration during shipment and post-manufacture handling. The end user must back-out each screw from its respective threaded aperture a sufficient distance in order to enable the placement of the electrical conductor or wire through the bore. This is a significant inconvenience and is particularly time consuming when many such connections have to be made for each device. Furthermore, when the screws are factory torqued for shipping, it is difficult for the end user to loosen the screws, and it is possible to strip or even break a screw when backing the screw out of its threaded aperture.
Thus, a need exists for a device and method which ensures clamping screws, for making electrical connections, are secured properly during shipping of the device, yet do not need to backed-out by the end user prior to making the electrical connections.
An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by a method of preventing vibration loosening of a clamping screw of a circuit protection apparatus. The circuit protection apparatus has a conductor receiving member including a conductor receiving opening for receiving an electrical conductor therein. The conductor receiving member has an aperture extending from a surface thereof into communication with the conductor receiving opening. An overall extent of the aperture includes threads. The method provides a clamping screw having a threaded shaft. The threaded shaft has a surface feature in the threads thereof near an end of the shaft. The clamping screw is inserted into the threaded aperture until the surface feature is in interference engagement with threads of the threaded aperture to hold the clamping screw in the threaded aperture, with the end of the shaft being disposed to permit access to the conductor receiving opening, such that the clamping screw need not be backed-out from the threaded aperture to provide access to the conductor receiving opening.
In accordance with another aspect of the invention, a circuit protection apparatus includes a conductor receiving member having a conductor receiving opening for receiving an electrical conductor therein. The conductor receiving member has an aperture extending from a surface thereof into communication with the conductor receiving opening. An overall extent of the aperture includes threads. A clamping screw has a threaded shaft and the threaded shaft has a surface feature in the threads thereof near an end of the shaft. The clamping screw is disposed in the threaded aperture with the surface feature in interference engagement with threads of the threaded aperture to hold the clamping screw in the threaded aperture. In this position, the end of the shaft is disposed to permit access to the conductor receiving opening such that the clamping screw need not be backed-out from the threaded aperture to provide access to the conductor receiving opening. The clamping screw is constructed and arranged such that when the clamping screw is tightened, the surface feature will move from engagement with the threads and become more easily to tighten, and the end of the shaft will move into the conductor receiving opening.
In yet another aspect of the invention, a clamping screw is provided for clamping an electrical conductor of a circuit protection apparatus. The circuit protection apparatus has a conductor receiving member including a conductor receiving opening for receiving an electrical conductor therein. The conductor receiving member has an aperture extending from a surface thereof into communication with the conductor receiving opening. An overall extent of the aperture is threaded. The clamping screw comprises a threaded shaft having a surface feature in the threads thereof near an end of the shaft such that when the end of the shaft is inserted into the threaded aperture, the surface feature becomes engaged with threads of the threaded aperture in an interference manner.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.